Electric utility companies have need to control devices on their distribution systems. For example, there is a need to turn off non-critical loads, such as water heaters and air conditioning equipment, during peak load conditions in order to save the relatively high cost of owning and operating peaking units; that is, generators whose purpose is to supply the additional power needed during peak load conditions. The loads to be controlled are owned and located in the customer's plant or home.
It is also desirable to reduce the voltage so as to decrease the power taken by the loads during periods of peak power.
During emergency load conditions, it is sometimes necessary to open circuit breakers and interrupt service beyond the circuit breaker until the emergency situation has ended.
Another use for control circuits is in the connecting and disconnecting of capacitors for the purpose of correcting the power factor of the system. In this application, a problem arises in that the economical place to measure power factor is at the substation; yet the optimum location for the capacitors is at several points along the distribution line feeding residential and industrial loads. The capacitors are typically located atop a utility distribution pole.
An article in the IEE Transactions on Power Apparatus and Systems, Volume PAS-99, No. 4, July/August, 1980, by B. F. Hastings, entitled "Ten Years of Operating Experience with a Remote Controlled Water Heater Load Management System at Detroit Edison" discusses certain background material concerning load management systems. As stated in the article, one early method of load management comprised a time-clock-controlled system for switching water heaters off during peak load periods. Subsequently, this system was changed to provide a radio communication system, which switched the loads in response to radio signals under the control of system operators. As discussed in the article, several other methods of power system control, including carrier telephone circuits and pilot wire, are known. However, as can be readily appreciated, the prior systems had several drawbacks, including the high cost of installing and operating a communication network from the substation to the large number of devices to be controlled.